Acoustic wave device

Abstract

An acoustic wave device includes a piezoelectric substrate and an IDT electrode. In the IDT electrode, at least one electrode finger includes a first portion and a second portion in an intersection region. The first portion is in direct contact with the piezoelectric substrate. The second portion is on the first portion such that a space in at least a portion of a central portion of the intersection region in the first portion is provided. A thickness of the first portion is smaller than a thickness of a busbar. A sum of the thickness of the first portion in a portion where the second portion is present and a thickness of the second portion is thicker than the thickness of the first portion in a portion where the second portion is not present.

What is claimed is: 
     
         1 . An acoustic wave device comprising:
 a piezoelectric substrate; and   an IDT electrode on the piezoelectric substrate; wherein   the IDT electrode includes:
 a plurality of electrode fingers; and 
 a busbar to which the plurality of electrode fingers are connected; 
   at least one electrode finger of the plurality of electrode fingers includes:
 in an intersection region at which the plurality of electrode fingers overlap each other when viewed from a propagation direction of an acoustic wave in the piezoelectric substrate; 
 a first portion in direct contact with the piezoelectric substrate; and 
 a second portion on the first portion; 
   the second portion is located on the first portion such that a space in at least a portion of a central portion of the intersection region in the first portion is provided;   a thickness of the first portion is thinner than a thickness of the busbar; and   a sum of a thickness of the first portion in a portion where the second portion is present and a thickness of the second portion is thicker than a thickness of the first portion in a portion where the second portion is not present.   
     
     
         2 . The acoustic wave device according to  claim 1 , wherein
 the at least one electrode finger further includes a third portion extending from the second portion over at least a portion of the central portion of the intersection region in a plan view from a thickness direction of the piezoelectric substrate.   
     
     
         3 . The acoustic wave device according to  claim 1 , wherein
 the at least one electrode finger includes a plurality of the second portions; and   in a plan view from a thickness direction of the piezoelectric substrate, a total area of portions between the plurality of second portions is larger than a total area of the plurality of second portions.   
     
     
         4 . The acoustic wave device according to  claim 1 , wherein the second portion is at an edge portion outside the central portion in the intersection region. 
     
     
         5 . The acoustic wave device according to  claim 1 , wherein the second portion includes aluminum. 
     
     
         6 . The acoustic wave device according to  claim 2 , wherein the third portion includes aluminum. 
     
     
         7 . The acoustic wave device according to  claim 1 , wherein
 the piezoelectric substrate includes:
 a piezoelectric layer; and 
 a support substrate on the piezoelectric layer. 
   
     
     
         8 . The acoustic wave device according to  claim 7 , wherein the piezoelectric substrate further includes a low acoustic velocity film between the piezoelectric layer and the support substrate, an acoustic velocity of a bulk wave propagating through the low acoustic velocity film being lower than an acoustic velocity of a bulk wave propagating through the piezoelectric layer. 
     
     
         9 . The acoustic wave device according to  claim 8 , wherein the piezoelectric substrate further includes a high acoustic velocity film between the low acoustic velocity film and the support substrate, an acoustic velocity of a bulk wave propagating through the high acoustic velocity film being higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer. 
     
     
         10 . The acoustic wave device according to  claim 1 , wherein a thickness of the piezoelectric substrate is less than about 2 λ, where λ is a wavelength determined by a pitch of the plurality of electrode fingers of the IDT electrode. 
     
     
         11 . The acoustic wave device according to  claim 1 , wherein the second portion is located on a portion of the first portion that is different from the central portion. 
     
     
         12 . The acoustic wave device according to  claim 1 , wherein
 the at least one electrode finger includes a plurality of the second portions;   at least one of the plurality of second portions is on a portion of the first portion different from the central portion; and   at least one of a remainder of the plurality of second portions on the central portion of the first portion.   
     
     
         13 . The acoustic wave device according to  claim 2 , wherein
 the at least one electrode finger includes a plurality of the second portions; and   in a plan view from a thickness direction of the piezoelectric substrate, a total area of portions between the plurality of second portions is larger than a total area of the plurality of second portions.   
     
     
         14 . The acoustic wave device according to  claim 2 , wherein the second portion is at an edge portion outside the central portion in the intersection region. 
     
     
         15 . The acoustic wave device according to  claim 2 , wherein the second portion includes aluminum. 
     
     
         16 . The acoustic wave device according to  claim 2 , wherein
 the piezoelectric substrate includes:
 a piezoelectric layer; and 
 a support substrate on the piezoelectric layer. 
   
     
     
         17 . The acoustic wave device according to  claim 16 , wherein the piezoelectric substrate further includes a low acoustic velocity film between the piezoelectric layer and the support substrate, an acoustic velocity of a bulk wave propagating through the low acoustic velocity film being lower than an acoustic velocity of a bulk wave propagating through the piezoelectric layer. 
     
     
         18 . The acoustic wave device according to  claim 17 , wherein the piezoelectric substrate further includes a high acoustic velocity film between the low acoustic velocity film and the support substrate, an acoustic velocity of a bulk wave propagating through the high acoustic velocity film being higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer.